This invention relates to meat processing. In particular, this invention relates to a method and system for tenderizing and sterilizing meat using electro-mechanical transducers to project opposing planar shock waves in meat.
Meat is an important source of nutrition in most balanced diets. Generally speaking, more desirable cuts of meat are in greater demand since they typically have higher fat content and are more tender than tougher cuts. However, consumers are becoming increasingly aware that excessive fat consumption is unhealthy, and they are looking for alternatives. Less-desirable cuts that are leaner and lower in fat content may be beneficial to health conscious buyers but the toughness of these cuts still makes them unattractive. In fact, many of these buyers indicate that leaner meats that are lower in fat content would be preferable if they were not so tough.
In addition to the health advantages of eating tougher, low fat meats, serving these cuts also is economically advantageous since tougher meat generally is less expensive than tender meat. Cost cutting in food procurements makes large scale purchases of low fat meat more attractive to large institutional and governmental buyers. However, the toughness of some cost effective cuts makes some of them substandard, or at least, less palatable, and serving such food is likely to have a demoralizing effect on workers. Since maintaining high moral is a significant factor toward high performance in the workplace and among personnel in the armed services, food should be tender and more palatable.
Meat has been tenderized by many different methods for years. The most common is simple mechanical pounding; however, pounding breaks the meat fibers, and changes the texture of the meat and its appearance. For example, pounding sirloin steak gives it an appearance and texture more akin to cheap hamburger than soft, tasty and more expensive sirloin. Lesser expensive cuts that are pounded also make this unappealing transition. Additionally, pounding is labor and mechanically intensive, prone to structural failure over relatively short operational cycles, and is slow.
Meat has been tenderized by aging. However, aging involves storing meat at controlled temperatures for three or four weeks. This is expensive since massive refrigerated storage space is required, and the flavor of the aged meat may be altered.
Chemical treatment of meats has also been used. By immersing the meat in a bath of enzymes or other chemicals over a period of time, meat can be tenderized. This method also takes some time but cuts aging time from three or four weeks down to around 10 days in a controlled refrigerated space. This method is also expensive due to the time and cost of refrigeration and constant replenishment of chemicals and enzymes. This method also changes the color, texture and flavor of the meat.
Other methods using ultrasonic massaging in water have been attempted and have proven largely ineffective due to the low power of the ultrasonic source and the low pressure waves produced. Essentially, low pressure waves from an ultrasonic source do not behave like shock waves, and as a result, low pressure waves fail to achieve the minimal levels of density of energy and power needed to effect the structural damage needed to tenderize.
Tenderizing has been attempted using shock waves generated by explosive charges. Explosive charges generate a spherical (point charge) shock wave in water to act upon a batch of meat. This batch method which has shown some promise but no positive commercial result is disclosed in U.S. Pat. Nos. 5,273,766 and 5,328,403. This batch method has numerous disadvantages: the use of explosives is dangerous and produces several direct and indirect products that are environmentally and commercially unacceptable. For this reason, meats have to be wrapped in airtight plastic bags prior to immersion into the water that fills the explosive chamber, and an inspection and decontamination procedure needs to be performed after detonation to ensure consumer health safety. In accordance with the process disclosed in these patents, detonation of the explosive charge sends a shock wave through the meat; but, since the meat is nearly the same relative density as water, the shock wave passes through yielding only marginal interaction with some meat fibers. Tests of this method have shown that detonation of explosives in a closed water-filled chamber produces a spherical shock wave that passes through the meat. A steel plate at the bottom of the closed, water filled chamber reflects the spherical shock wave back through the meat a second time after it passes through the meat a first time. In each pass, the shock wave is in the form of a spherical wave that only marginally interacts with some meat fibers. This process is difficult to control and lacks uniformity of tenderizing. In addition, there are obvious operational and liability risks of using chemical explosives, dealing with the noxious residue of each chemical explosion, and potentially contaminating the meat. The geometrical arrangement of the chamber disclosed in the above referenced patent is inefficient. The generation of destructive interferences of shock waves within the meat is indeterminable since spherical shock waves generated by the explosive charge rebound and reverberate off the steel walls of the container and the bottom plate hopefully where intended. This questionable effectiveness has further negated the potential value of the disclosed method of these patents. Furthermore, due to this inefficiency, large amounts of explosive must be used in order to get marginal improvement in tenderness. In addition, a large lid having associated shock absorbers and dampers must be used to contain the large detonation in the chamber. Any tenderizing by the explosive methods of processing batches usually is the result of brute force application of plenty of explosives in a single shot that must be reloaded after each shot. Thus, batch processing by detonating explosives is substantially more labor intensive than the efficient use of mechanically generated shock waves in the continuous process of this invention.
Thermal sterilization and high pressure sterilization methods are discussed in U.S. Pat. No. 5,588,357. Historically, some thermal sterilization methods and high-pressure sterilization methods have been used for sterilizing some kinds of food. In the thermal sterilization method, food is heated at a predetermined temperature through thermal conduction so that the food can be sterilized. Unfortunately, the thermal sterilization method results in degeneration of protein in food because of heating. In addition, thermally sterilized food sometimes emits a smell unique to thermal sterilization. In the high-pressure sterilization method, food is subjected to a high pressure, typically hundreds to thousands times atmospheric pressure to be sterilized. A conventional apparatus for the high-pressure sterilization method is large, and its sterilizing ability is poor since the apparatus is incapable of performing successive sterilizations.
The shockwave sterilizer of the '357 patent has an elastic container for containing food, a shock wave source which is disposed to face the elastic container, and a pressure transfer medium which is interposed between the shock wave source and the elastic container. A spherical shock wave emitted from the shock wave source is transferred to the elastic container through the pressure transfer medium. The shock wave is first applied onto food contained in the container and an expansion wave is next applied onto the food after a small time delay. When the shock wave and the expansion wave are applied, differences in the shock impedance of materials (of each individual cell of bacteria) create differences in the pressure change within each cell of bacteria. This in turn creates non-equilibrium force in each cell, and as a result, the cell is destroyed and the food is sterilized. The time required for radiating the shock wave is only a few hundred microseconds so that there will be no chemical change due to a high temperature or a change in the pressure such as thermal degeneration of protein or the like. Therefore, food can be sterilized at a normal temperature, and reliable sterilization is possible without any large scale and complex apparatus. This approach also requires overcoming the problem of bacterial contamination of the shock wave sterilizer, and is done in '357 by using a vaporizing electrode. But, the vaporizing electrode might be a source of meat contamination unless an elastic (plastic) barrier is used. The elastic barrier is included to withstand the peak impulse shock wave of the vaporizing electrode which may reach 6,000 psi, without rupturing. Because of this high peak impulse shock wave of the vaporizing electrode, it is conceivable that the plastic container will leak. This may require an expensive quality assurance process to ensure high confidence levels that the plastic container will not leak under all operational conditions.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for an acceptable method of and means for tenderizing and sterilizing meat while maintaining its nutritional value.